Bone anchoring nail

ABSTRACT

A bone anchoring nail is provided having a threadless shaft with a free end, a head opposite to the free end, the head having a substantially U-shaped recess for accommodation of a rod or a rod-shaped element, a longitudinal bore extending through the shaft and opening towards any one of the head and the free end and a plurality of openings extending through the wall of the shaft and being in communication with the bore. The bone anchoring nail allows quick insertion and reliable fixation enhanced by the in-growth of blood vessels.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of U.S. Provisional PatentApplicant Ser. No. 60/858,175, filed Nov. 10, 2006, and claims priorityfrom European Patent Application EP 06023443.2, filed Nov. 10, 2006, thedisclosures of which are incorporated herein by reference.

BACKGROUND

The present invention relates to a bone anchoring nail. In particular,it relates to a bone anchoring nail having a shaft with a longitudinalbore and a plurality of openings in the wall of the shaft, and a headwith a substantially U-shaped recess for accommodation of a rod. Thebone anchoring nail can be used, for example, for anchoring a spinal rodin the pedicles of adjacent vertebrae for stabilizing the spinal columnor it can be used in any other type of bone anchor application using arod or a rod-shaped element.

A bone anchoring device in form of a bone screw comprising a screw headand a threaded shaft, wherein an axial bore is provided which isconnected to the outside through a plurality of radial bores is knownfrom WO 01/26568. Bone cement can be injected through the bone screw andinto the bony tissue surrounding the threaded shaft. US 2004/0147929 A1discloses a bone anchoring device having a tubular element having asection with a bone thread on its outer wall, a tip and a head which canbe connected to the tubular element, wherein the head comprises aU-shaped recess for receiving a rod. The insertion of such a boneanchoring device is accomplished by screwing-in which is force and timeconsuming. Further, during screwing, forces act onto the bone which canbe too large in certain situations, for example in the case of olderand/or weak bones.

US 2004/0220575 A1 discloses a bone anchoring element for anchoring anexternal device in the bone. The bone anchoring element comprises a headwhich is connectable to the external device and a shaft connected to thehead, wherein the shaft has a predetermined section with a bone threadand at least one bone thread-free section within said predeterminedsection. The bone anchoring device can be pushed into a predrilled holein the bone and then turned so as to allow anchoring by means of thebone thread. The anchoring device can be unscrewed due to the presenceof the bone thread. In a specific embodiment the shaft comprises alongitudinal bore with radial bores leading to the outside for thepurpose of allowing the introduction of a medical agent or bone cementinto the pre-drilled hole.

U.S. Pat. No. 5,743,912 and JP 09149906 A disclose medical implantscomprising a shaft with a longitudinal bore and radial openings and athreaded section at one end.

US 2006/0089642 A1 describes an implant for vertebrae and other boneswhich is formed as an elongated cylindrical body with a series ofperforations penetrating the cylinder wall and communicating with thecylinder bore. The bore may be filled with a bone growth mixture. Theimplant is not suitable for connection with a spinal stabilization rod.

For certain clinical requirements, in particular for the stabilizationof weak osteoporotic bone, in pediatric surgery, in surgery of thecervical spine or in neurosurgery, there is a need for bone anchoringdevices which can be connected to an external stabilization rod orrod-shaped element, wherein the bone anchoring devices can be insertedeven more quickly and with lower insertion forces than the known deviceswhile providing a safe fixation which is comparable to that of screws.

SUMMARY

The bone anchoring nail according to the invention allows a fastinsertion into a core hole which is provided in the bone in advance. Areliable and lasting fixation is accomplished by ingrowth of vesselsinto the openings followed by newly formed bone into the openings and/orby the injection of bone cement through the longitudinal bore whichexits through the openings, hardens and connects the nail to thesurrounding bone material.

The bone anchoring nail is specifically applicable to minimally invasivesurgery (MIS), to spinal surgery and to the stabilization of long bones.

Further features and advantages of the invention will become apparentand will be best understood by reference to the following detaileddescription of embodiments taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective exploded view of a bone anchoring nailaccording to a first embodiment.

FIG. 2 shows the bone anchoring nail according to FIG. 1 in an assembledstate connected to a rod.

FIG. 3 shows a side view of the bone anchoring nail with the rodaccording to the first embodiment in a direction along the rod axis.

FIG. 4 shows a sectional view of the bone anchoring nail with the rodaccording to the first embodiment, the section being taken along the rodaxis.

FIG. 5 shows an exploded perspective view of the bone anchoring nailaccording to a second embodiment.

FIG. 6 shows the bone anchoring nail according to the second embodimentin an assembled state connected to a rod.

FIG. 7 shows a sectional view of the bone anchoring nail of the secondembodiment connected to a rod, the section be taken along the rod axisand a schematic view of the in-growth of vessels.

FIG. 8 shows an injection device for injecting medical treatment agentsor bone cement.

DETAILED DESCRIPTION

A bone anchoring nail according to a first embodiment of the inventionis described with reference to FIGS. 1 to 4. The bone anchoring nailcomprises a shaft 1 having a free end 2 and head 3 opposite to the freeend 2. A coaxial bore 4 extends through the shaft from the end where thehead 3 is located up to a distance from the free end 2. The diameter ofthe coaxial bore 4 is such that the shaft has sufficient strengthagainst failure.

A plurality of openings 5 extend in a radial direction from the bore 4through the wall of the shaft 1 to the outside. The cross-section of theopenings is preferably circular or otherwise rounded. The openings canbe arranged in a regular manner, such as, for example, incircumferential rows wherein one row is offset with regard to anotherrow such as to provide a uniform distribution of openings in a sectionof the shaft 1. As shown in the drawings, there can be a section of theshaft 1 which is adjacent to the head 3 where no openings are provided.The number and arrangement of the openings is varied according to theclinical requirements. The diameter of the openings is at least as largeso that blood vessels from the surrounding bone material can grow-infollowed by the formation of new bone into the openings. Also, thediameter of the opening is selected such that bone cement and/or medicaltreatment agents can exit through the openings without clogging. At theouter wall of the shaft 1 a countersink area (not shown) around theopenings can be provided to facilitate in-growth. The openings 5 areshown to extend in a radial direction with respect to the shaft axis M.However, some or all of them may also extend in a direction including anangle with the axial bore which is different from 90°. The length of theshaft is selected so as to be suitable for the specific application.

The free end 2 is shaped as a tip. However, free end 2 also can be flat.The shaft 1 can taper to the free end 2 in a section 6, for example, itcan taper in a conical shape. The coaxial bore 4 can also extend overthe full length of the shaft 1 up to the free end 2 such that itprovides an opening at the free end 2. Also, the tip can be provided asa separate part connectable to the shaft 1. In this case, the coaxialbore 4 may be closed by connecting a separate tip to the shaft. As shownin the drawings, the outer surface of the shaft 1 is threadless. Inaddition, the outer surface of the shaft 1 can be treated to provide anenhanced fixation or to enhance slidability of the shaft in the corehole. For example, the outer surface can be roughened to enhancefixation or coated with a material promoting in-growth. In anotherexample, the surface can be coated or polished or otherwise treated toenhance slidability to facilitate insertion.

The head 3 is, in the embodiment shown, substantiallycylindrically-shaped with an outer diameter which is larger than thediameter of the shaft 1. The head 3 comprises a substantially U-shapedrecess 7 and a coaxial bore 8 which extends through the head and is incommunication with the coaxial bore 4 of the shaft. By means of theU-shaped recess 7 two free legs 9, 10 are formed which are provided withan internal thread 11. The diameter of the U-shaped recess 7 is suchthat a rod 12, used for connecting several of the bone anchoring nailswith each other, can be inserted. The rod 12 is secured by a lockingelement, for example by an inner screw 13 which can be screwed-inbetween the legs 9, 10 and which presses onto the rod.

In the embodiment shown the head 3 and the shaft 1 are designed as asingle part. However, the head 3 and the shaft 1 can also be designed asseparate parts, wherein the head 3 and the shaft 1 can be rigidlyconnected with each other so as to form a rigid monoaxial connection.Alternatively, the head 3 and the shaft 1 can be rotatably connected,the rotation axis being the shaft axis.

The locking element can be realized otherwise than by an inner screw 13.For example, a combination of an outer nut which cooperates with anouter thread on the head 3 and an inner screw can be provided.Alternatively, another locking mechanism is conceivable, for example, abayonet coupling between the locking element and the head.

The bone anchoring nail is made of a biocompatible material, such astitanium or a titanium alloy or a biocompatible plastic material. It canalso be made from a shape memory alloy.

In operation, first, a core hole is prepared in the bone area where thebone anchoring nail is to be anchored. The inner diameter of the holecorresponds to the outer diameter of the shaft or is slightly smaller.The shaft 1 is then pushed or pressed into the core hole. If the shaft 1is pressed into the core hole it holds due to the frictional forces. Theaction of inserting the shaft into the hole is considerably less timeconsuming than screwing a bone screw into the bone, even if apre-drilled hole is used for the bone screw. Hence, the bone anchoringnail can be used in such clinical situations, in which a very quickinsertion is necessary and/or in which weakness of the bone materialdoes not allow the application of large insertion forces which may occurin the case of using a bone screw.

After inserting at least two bone anchoring nails they can be connectedvia the rod. The rod is fixed by tightening the inner screw. The boneanchoring nail can also be combined with conventional monoaxial bonescrews which are used for connection with rods.

After some time blood vessels may begin to grow-in through the openings5 into the coaxial bore 4 followed by the formation of new bone, therebyenhancing the fixation. For further enhancing the fixation a bone cementsuch as for example Polymethylmethacrylate (PMMA) or TricalciumPhosphates (TCP) can be introduced through the bore 8 of the head andthe longitudinal bore 4 of the shaft before inserting the rod. The bonecement is in a substantially fluid form and exits through the openings5. When it hardens, it firmly connects the shaft 1 with the surroundingbone material.

A second embodiment is shown in FIG. 5 to 7. The second embodimentdiffers from the first embodiment in that the head and the shaft areconfigured as separate parts which are pivotably connected so as toallow a polyaxial adjustment. Parts which are identical to the firstembodiment are designated with the same reference numerals. The shaft 1′differs from the first embodiment in that it has a sphericalsegment-shaped end section 1 a through which the longitudinal bore 4extends. On its free end the spherical segment-shaped end section 1 acomprises a recess 1 b for engagement with a screwing-in tool.

The head 3′ is formed as a separate part. It has, like the head 3 of thefirst embodiment, a substantially cylindrical shape with a substantiallyU-shaped recess 7 and a coaxial bore 8 by means of which two legs 9, 10are formed on which an internal thread 11 is provided. The head 3′ has alower side 3 a with an opening 3 b which is dimensioned such thatspherical segment-shaped head 1 a cannot fall out in the assembledstate. Between the bore 8 and the opening 3 b a seat 3 c for thespherical segment-shaped end section 1 a is provided. In the assembledstate, the shaft 1′ can pivot relative to the head 3′.

The bone anchoring nail according to the second embodiment furthercomprises a pressure element 14 which is substantiallycylindrically-shaped with a coaxial bore 15 and a spherical section 16suitable to press on to the end section 1 a. In the embodiment shown thepressure element 14 has a substantially U-shaped recess 17 opposite tothe spherical section 16 for receiving the rod 12. The pressure element14 can be secured within the head 3′ against rotation and againstfalling out. Preferably, the shaft 1′, the head 3′ and the pressureelement 14 are preassembled.

Use of the bone anchoring nail according to the second embodiment issimilar to that of the first embodiment. The bone anchoring nailaccording to the second embodiment allows a polyaxial adjustment of thehead 3′ with respect to the shaft 1′. The angular position of the shaft1′ relative to the head 3′ is locked by pressing the pressure element 14onto the spherical segment-shaped end section 1 a which presses thespherical segment-shaped end section 1 a against the seat 3 c. Lockingis accomplished by tightening the inner screw such that the rod 12 isfixed and transmits the force onto the pressure element 14 which thenblocks the spherical segment-shaped end section 1 a.

In a modification, the spherical segment-section 1 a of the shaft 1′ andthe rod 12 can be locked independently from each other.

FIG. 7 schematically shows the in-growth of blood vessels through theopenings 5. The vessels extend through the openings and can furthercontinue to grow in the coaxial bore 4.

FIG. 8 schematically shows an injection instrument 20 for injecting bonecement or a medical treatment agent into the shaft 1, 1′. The injectioninstrument 20 comprises a reservoir 21 for the agent or the bone cement,an injection tube 22 and an actuator 23 for actuating the injection. Theinjection tube 22 has an outer diameter which is smaller than thediameter of the coaxial bore 4 such that it can be introduced to such anextent into the coaxial bore 4 that it reaches the vicinity of theopenings.

While a particular form of the disclosure has been illustrated anddescribed, it will be apparent that various modifications can be madewithout departing from the spirit and scope of the disclosure.Accordingly, it is not intended that the disclosure be limited, exceptas by the appended claims.

1. A Bone anchoring nail comprising: a threadless shaft with a free end,a head opposite to the free end, the head having a substantiallyU-shaped recess for accommodation of a rod-shaped element, alongitudinal bore extending through the shaft and opening towards atleast one of the head and the free end and a plurality of openingsextending through the wall of the shaft and being in communication withthe bore.
 2. The bone anchoring nail of claim 1, wherein the bore isopen towards the head and closed at the second end.
 3. The boneanchoring nail of claim 1, wherein the shaft has a substantiallycylindrical shape.
 4. The bone anchoring nail of claim 1, wherein theopenings have a round cross-section.
 5. The bone anchoring nail of claim1, wherein the openings extend in a radial direction from the shaftaxis.
 6. The bone anchoring nail of claim 1, wherein the outer surfaceof the shaft is any one of treated, roughened and coated to enhancefixation.
 7. The bone anchoring nail of claim 1, wherein the shaft andthe head are mono-axially connected.
 8. The bone anchoring nail of claim1, wherein the shaft has a spherical segment-shaped end section and thehead is a separate part which is provided with a seat for pivotablyholding the end section.
 9. The bone anchoring nail of claim 8, furthercomprising a pressure element between the rod and the end section, thepressure element locking the end section against the seat when pressureis exerted.
 10. The bone anchoring nail of claim 1, further comprising alocking element for locking the rod-shaped element in the recess, thelocking element cooperating with the head.
 11. A method of anchoring abone anchoring nail to a bone, the method comprising: creating a corehole in a bone; and inserting a threadless shaft into the core hole, theshaft having a free end and a head opposite to the free end, the headhaving a substantially U-shaped recess for accommodation of a rod-shapedelement, the shaft having a longitudinal bore extending through theshaft and opening towards at least one of the head and the free end anda plurality of openings extending through the wall of the shaft andbeing in communication with the bore.
 12. The method of claim 11,further comprising inserting bone material in the longitudinal bore. 13.The method of claim 11, further comprising inserting a rod-shapedelement in the U-shaped recess and securing the rod shaped element inthe U-shaped recess.
 14. The method of claim 11, further comprising:inserting a pressure element in the U-shaped recess, wherein thepressure element is configured to receive the rod-shaped element,wherein the shaft has a spherical segment-shaped end section and thehead is a separate part which is provided with a seat for pivotablyholding the end section, wherein the pressure element is configured tolock the end section against the seat when pressure is exerted;inserting a rod-shaped element in the recess, the rod-shaped elementdisposed on the pressure element; locking the spherical segment-shapedend section in the seat by exerting pressure with the pressure element;and securing the rod-shaped element in the recess.